A comparison of the climate response to increased carbon dioxide simulated by general circulation models with mixed-layer and dynamic ocean representations in the region of South America

The patterns of climate change in the South American continent and surrounding oceans simulated in two sets of general circulation model (GCM) climate experiments under an enhanced greenhouse effect, are compared. One set is composed of doubled CO2 concentration equilibrium climate experiments, performed by five GCMs with mixed-layer (slab) ocean representation (SGCM). The other set includes transient climate experiments simulating increasing CO2 concentration, performed by five coupled GCMs with dynamic ocean representation (CGCM). The variables considered are near-surface temperature, mean sea-level pressure, and precipitation. A statistical measure of performance, which combines the complementary information of the root-mean-square error and pattern correlation, is used to assess model capability in control runs, and it is later applied in calculating weighted mean variation fields (2×CO2−1×CO2 experiments). Climate change patterns with consensus among model results are analysed with regard to their physical consistency. The CGCM experiments confirm previous results of SGCM experiments, i.e. the precipitation increase in the eastern equatorial Pacific over the Inter Tropical Convergence Zone, extending toward the north-western part of the continent. They also confirm the negative precipitation trend between the Orinoco and the Amazon rivers in the northern part of the continent. The strengthening of the Pacific anticyclone on its south-eastern side next to the continent is seen in both sets of experiments, but the rainfall decrease and continental warming in subtropical latitudes is more extensive in CGCM than in SGCM experiments. The rainfall increase along the South Atlantic Convergence Zone in the eastern part of the continent during the Southern Hemisphere summer is another persistent feature. The CGCMs simulate lower warming rates in high latitudes than SGCMs, a feature which extends northward along the western coast of the continent in the former experiments. The intensification of the latitudinal temperature gradient between 35° and 50°S in oceanic regions surrounding the continent, and the strengthening of the mid-latitude meridional pressure gradient, is concurrent with an enhanced rainfall rate over the storm track extending along 50°S during June, July and August.